1. Field of the Invention
The present invention relates to a spacer provided in a container including an electron-emitting device, an image-forming apparatus comprising an electron-emitting device, an image-forming member, and a spacer, in a container, and a manufacturing method thereof.
2. Related Background Art
As an image-forming apparatus using an electron-emitting device, an electron beam display panel of a flat type has been conventionally known in which an electron source substrate on which a number of cold cathode electron emitting devices are formed is opposed in parallel to an anode substrate comprising a transparent electrode and a fluorescent member and which is exhausted to be in a vacuum.
Among image-forming apparatuses of this kind, an image-forming apparatus using a field emission electron-emitting device is, for example, disclosed in I. Brodie, "Advanced technology: flat cold-cathode CRTs", Information Display, 1/89, 17(1989). Another image-forming apparatus using a surface conduction electron-emitting device is, for example, disclosed in Japanese Patent Application Laid-open No. 7-45221.
An electron beam display panel of a flat surface type can realize a lighter weight and a larger screen in comparison with a cathode ray tube (CRT) display apparatus which is widely used at present, and can provide an image with a higher luminance and a higher quality in comparison with a flat type display panel including, for example, a plasma display or a liquid crystal display.
FIGS. 14 and 15 are views schematically showing a structure of a conventional flat type electron beam display panel, as an example of an image-forming apparatus using an electron-emitting device. See Japanese Patent Application Laid-open No. 8-180821. FIG. 15 is a cross-section cut along line 15-15 in FIG. 14.
The structure of the conventional flat type electron beam display panel shown in FIGS. 14 and 15 will now be explained in details below. In these figures, reference 141 denotes a rear plate on which an electron source substrate 144 is provided, and reference 142 denotes a face plate as an anode substrate. These substrates are connected with each other and also with a supporting frame (or outer frame) 143 by a connecting portion made of frit glass or the like, thereby forming a vacuum envelope. Reference 145 denotes an electron-emitting element. Reference 146a (e.g., a scanning electrode) and a reference 146b (e.g., a signal electrode) are electrode wires and are connected to the electron-emitting device 145. References 147a and 147b denote a scanning line and a signal line, respectively. A reference 148 is a glass substrate as a base member of the face plate. Reference 149 denotes a fluorescent member, and reference 150 denotes a metal back. Reference 151 is a spacer which maintain the rear plate 141 and the face plate 142 with a predetermined distance inserted therebetween, and is provided as a support member against an air pressure.
To form an image by the electron beam display panel, scanning lines 147a and signal lines 147b arranged in a matrix are sequentially applied with a predetermined voltage, to selectively drive predetermined electron-emitting devices 145 positioned at cross points of the matrix. Electrons emitted therefrom are irradiated onto a fluorescent member 149 to obtain a luminance point at a predetermined position. Note that a metal back (anode) 150 is applied with a high electric potential such that a positive potential is obtained with respect to devices 145, in order to accelerate emitted electrons to obtain a luminance point with a higher luminance.
The image-forming apparatus constructed in the structure as described above, particularly, uses a fluorescent member of a low price having a high light-emission efficiency, which is used in a current CRT display, and an acceleration voltage of several kV to several tens kV is applied to obtain a high luminance and to improve color performance. However, a distance d between the rear plate 141 and the face plate 142 must be set to 1 mm or more in consideration of an insulating break-down in a vacuum (i.e., a discharge).
Meanwhile, in the case of using a field emission electron-emitting device as an electron-emitting device as described above, a convergence electrode may be provided or the distance d between the rear plate 141 and the face plate 142 may be reduced, to form an image, in response to a problem of convergence of an electron beam. The voltage applied in this case falls within a range from several hundreds V to several kV although the voltage depends on the performance of a fluorescent member, the presence or absence of a metal back, and the distance between the face plate and the rear place. Therefore, the distance d between the rear plate 141 and the face plate 142 (or the distance between the wire 147b and the metal back 150, more specifically) is generally set to one hundred .mu.m to several mm, so that a insulating break-down in a vacuum (i.e., a discharge) might not take place.
In order to reduce deformation of substrates caused by a pressure difference between the vacuum inside an envelope and the external air pressure, the rear plate substrate 141 and the face plate substrate 148 must be thickened as the display area of a display panel increases. An increase in thickness of the substrates causes an increase in weight of the display panel and deformation viewed from an oblique direction. Therefore, by providing a spacer 151, loads to the strength of the substrates 141 and 148 can be reduced, and a weight reduction, a low cost, and a large screen can be achieved, so that advantage of a flat type electron beam display panel can be sufficiently performed.
Material used for the spacer 151 requires the following conditions. A sufficient air pressure strength (or compressive strength) is ensured and a high aspect ratio (i.e., the ratio between the height of the spacer and the cross-sectional area) is obtained so that the spacer can be arranged in an image-forming apparatus, i.e., the material is strong against a break-down, deformation, and bending caused by compression; the material has a heat resistance enough to withstand heating steps in manufacturing steps and high-vacuum formation steps and matches with heat expansion coefficients of the substrates of the display panel, a supporting frame, and the like; the material is highly resistive material or insulating material having a dielectric strength enough to withstand an application of a high voltage; the material has a low gas discharge rate to maintain a high vacuum; and the material can be processed with high size precision and ensures a high mass-productivity. Generally, glass material is used.
On the other hand, spacers which are improved in creeping discharge breakdown voltage by forming irregularity on their surfaces are exemplarily described in Japanese Patent Application Nos. 8-241667, 8-241670 and 8-315726. It is also described that secondary electrons emitted by incident electron beams to such spacers can be captured by a concave surface to further improve the creeping discharge breakdown voltage and that such spacers are manufactured by molding glass, ceramic or polymer materials.
Glass material generally used has relatively excellent mechanical strength, heat characteristics, and disorption gas characteristics. In addition, such glass material has an excellent process ability and an excellent mass-productivity and is therefore generally used as spacer material.
Meanwhile, there is a case in which some electrons emitted from an electron-emitting device enter into the surface of a spacer. As a result, the spacer surface is charged and greatly reduces the creeping discharge breakdown voltage or the potential of the surface changes and distorts the electric field in the vicinity of the surface, so that courses of electrons from the electron source are adversely affected, resulting in a phenomenon such as a color dislocation which degrades the image quality.
As for a method of avoiding degradation of the quality of images such as a color dislocation caused by a charged spacer as described above, for example, Japanese Patent Publication No. 7-99679 discloses a method of forming a spacer from conductive material having a high resistance which allows a slight current to flow. An apparatus disclosed in this publication comprises a group of electrodes between a face plate and an electron source. These electrodes are convergence electrodes and deflection electrodes for purposes of focusing of electron beams and deflection thereof and are applied with a potential in accordance with those purposes.
Another example of an image-forming apparatus which does not have such a group of electrodes is disclosed in Japanese Patent Application Laid-Open No. 5-266807. In this application, electrodes, wires, and anode electrodes on an electron source substrate on which a plurality of electron-emitting devices are arranged are connected with a spacer member having an electric conductivity, to prevent charging.
Meanwhile, a spacer made of resin or the like such as polyimide is known, other than spacers made of inorganic material such as glass or the like. For example, "Advanced technology: flat cold-cathode CRTS" (Information Display 1/89, pages 17 to 19 and U.S. Pat. No. 5,063,327, Mr. Ivor Brodie discloses a spacer using polyimide. This is a technique in which photosensitive polyimide is applied to a substrate by a spin method and vacuum baking is carried out through a photolithography step (including mask exposure, development, and washing) after pre-baking. Finally, a polyimide spacer having a height of 100 .mu.m is formed on the surface of a substrate. Further, U.S. Pat. No. 5,371,433 may be cited as an example using photosensitive polyimide. This U.S. Pat. No. 5,371,433 realizes a spacer having a height of about 1 mm by layering two layers of polyimide each having a height of 500 .mu.m and formed through a photolithography step (including mask exposure, development, and washing), likewise.
Japanese Patent Application Laid-Open No. 6-162968 discloses, for example, a method of coating low secondary electron-emitting material or the like in order to avoid emission of electrons from the inner wall of a spacer plate provided between an address system and a fluorescent screen, in a flat panel type image-forming apparatus in which secondary electrons generated in a plurality of ducts are picked up by an address system and are made to collide into a fluorescent screen.